Turbines, defined to be a system where the momentum of fluid stream is directed against rotatably mounted vanes, have been in existence for thousands of years in one form or another.
In modern form, a turbine typically includes a combustion chamber for generating a high pressure volume of gas, a nozzle having a converging-diverging channel which shape converts the energy of a gas stream emerging from the combustion chamber from having a large potential component, (large pressure) to having a large kinetic component and a rotating vane section against which the high velocity stream is directed to transfer the kinetic energy of the gas to the rotational energy of the blades. The increase in the kinetic component (increased velocity of the gas stream) is accomplished in the nozzle by passing the gas from an entry section having a large sectional area through a convergent area having a smaller sectional area.
When effectively most all of the conversion from potential to kinetic energy takes place in one “stage”,(i.e., one rotating wheel energized by one nozzle,) the turbine is said to operate by “impulse” and the turbine is therefore known as an impulse turbine.
A limit to efficiency of an impulse turbine is imposed by a property of the gas media when a certain “critical pressure”, drop across the nozzle is exceeded, then the volume of discharge of gas through the nozzle is constant in spite of increasing ratio of inlet pressure to outlet pressure. Consequently, there is an inherent limit to the amount of energy that can be extracted from the flow of the gas through a nozzle that converts potential to kinetic energy.
In order to overcome this natural limitation, the “reactive” turbine has been developed which includes a gang of nozzle-turbine stages all operating in series. With each stage, the gas stream is subject to a succession of potential to kinetic changes accompanied by successive reduction of energy of the stream so as to extract a maximum total energy from the gas stream before discharging the gas stream to the environment.
Each stage of the reactive turbine includes a stationary section which functions as a nozzle in converting pressure to velocity and a rotating section which converts some of the kinetic energy of the gas stream to kinetic energy of the respective rotating section.
The reactive turbine inherently has a limited efficiency due to losses of energy arising from turbulence of the high speed stream passing through the rotating section and frictional losses of the gas stream passing across the walls of the “stationary” section. The loss of energy due to friction with stationary surfaces increases with the number of stationary sections.
The typical rotating section of the turbine includes blades against which surfaces the gas stream is directed causing the wheel to which the blades are attached to rotate. If a gas molecule, travelling at high speed with a velocity component parallel to the blade surface, could be somehow made to “stick” to the blade surface, then all of the kinetic energy would be transferred to the rotating blade. However, since the molecule does not “stick” to the blade surface, it leaves only part of its kinetic energy and consequently, turbine systems are designed with a number of stages for successively absorbing the energy of the stream. These constructions are expensive. Another characteristic of turbine systems is that very large velocities of the gas stream are required to transport a useful rate of power because of the low density of the gas stream. Consequently, the turbines are characterized by much larger rotational velocities than with other types of engines such as the internal combustion engines. Furthermore, the high velocities go hand in hand with a requirement for higher operating temperatures which generally requires the use of more expensive materials and designs in which heat dissipation is an important consideration.
In order to avoid many of these problems, particularly complexity of design, the “vaneless” turbine was introduced around the beginning of the twentieth century. The vaneless turbine is simply a stack of disks rotatably mounted and closely spaced from one another on a common axis in which a gas stream from a nozzle is directed generally tangentially in the space between the disks. The frictional drag of the stream of gas across the surfaces of the disks causes the disks to rotate. In contrast to the impulse type of turbine having blades, the greater the frictional force of the gas stream against the disk surfaces, the greater will be the rate of transfer of kinetic energy from the gas stream to the rotating disk and, hence, the greater will be the efficiency of the turbine. In fact, the limitation of efficiency of the disk turbine is the limitation of the magnitude of friction between the gas stream and the disk surface and the length of the path. Another inherent limitation is the low density of the gas stream requiring that fast velocities (implying large temperature of the gas stream) is required for effective energy carrying capacity.
In summary, the efficiency of the typical impulse turbine is limited by the amount of work required to compress the gas for entry into the compression chamber and by the energy losses due to friction of the gas passing through the nozzle and turbulence of the gas passing through the rotating section. The efficiency of the typical vaneless type of turbine system is limited by the energy required to compress the gas prior to in a combustion chamber, the limit on the frictional interaction between the gas stream and the walls of the disk coupled with the limited path length of the gas stream across the disk surfaces before discharge of the gas stream to the environment.
For the purposes of this specification, it is useful to review the action of the steam cleaner which is well known in the market place. the steam cleaner includes a reservoir of water, a heater for heating the water and a nozzle that directs combination of steam and water droplets against a surface to be cleaned. The device uses steam expansion to propel water droplets at near the boiling temperature of water at a considerable velocity.
In the typical steam cleaner, water is heated to 325° F. in a pressure range between 90 to 250 psi. Water heated to 325 degrees remains liquid at any pressure over 80 psi. (the saturated pressure of steam at that temperature. When water that is pressurized greater than 80 psi and heated to 325° F. passes through the nozzle thereby suddenly reducing the pressure, the water is suddenly cooled to 212° F. by vaporizing a portion of its volume (5 to 15%) to steam. The steam vapor, formed in an appropriately designed nozzle including an expansion nozzle placed past the pressure orifice, propels and directs the water as droplets from the mouth of the nozzle.
When water vaporizes, it expands to 27 times its former volume. This expansion is directed by the conical steam nozzle so that the nozzle serves as a propulsion chamber. The expansion nozzle both creates an explosive effect and directs the energized water droplets.
There are two types of steam cleaners: “vapor” cleaners and “hydraulic pressure combination”cleaners (HPC).
The vapor cleaner relies almost entirely on vaporization in the expansion nozzle for propulsion of the cleaning solution. The pump generally produces only enough pressure (about 80 psi) against the solution to keep it from boiling. in the coil.
The HPC cleaner operates in the range 150 to 250 psi. At this greater pressure, a smaller fraction of water “flashes” to steam but the higher pressure adds the additional energy to the water droplets. Typically, 5 to 7% water flashes to steam in a HPC cleaner. The size of the water droplets decreases as the size of the pressure orifice on the nozzle is decreased. The larger water droplets create more impact on the surface being impinged by the water.